We performed atomistic modeling to study structural and mechanical properties of materials. We used density functional theory (DFT) for all the studies presented and constructed a method for quickly optimizing semi-empirical modified embedded atom method (MEAM) potentials. In our first study, we show that the reconstruction model in the literature for GaSb(001) is not predicted to have the lowest surface reconstruction energy. A modification was proposed that improves the energy. The second study tries to validate a crystal structure for the Φ Phase of Al-Mg-Zn. The third study deals with plain carbon steel, including some microalloying of Vanadium and vacancy assisted diffusion of Fe in Cementite(Fe3C). In the fourth study, we show a method for optimizing a MEAM potential. The code written is specific to hexagonal closed packed structures and was applied to a Magnesium potential.